Radio-frequency system for a magnetic resonance apparatus

Abstract

A radio-frequency system for a magnetic resonance apparatus has a local coil, a body coil, and an impedance adjusting shield. The body coil is wirelessly power-coupled with the local coil such that the body coil serves as a transmitting coil for radio-frequency signals and the local coil serves as a receiving coil for magnetic resonance signals. The local coil is disposed in an internal cavity of the impedance adjusting shield. An impedance of the local coil is adjusted by the impedance adjusting shield so as to match the impedance of the local coil and the body coil. The impedance adjusting shield has a frequency modulation element that adjusts the resonance frequency of the local coil. The body coil couples power to the local coil, and the impedance adjusting shield effectively reduces energy transmission efficiency loss caused by reflection, thereby improving energy transmission efficiency.

The invention claimed is: 
     
       1. A radio-frequency (RF) system comprising:
 a local RF coil comprising an inductively coupled coil and a resonator; 
 a body RF coil wirelessly power-coupled with said local RF coil in order for said body RF coil to serve as a transmitting coil for RF signals, and in order for said local coil to serve as a receiving coil for magnetic resonance signals resulting from said RF signals; and 
 an impedance adjusting shield comprising an internal cavity and a frequency modulation element, said local RF coil being disposed in said internal cavity with an impedance of the local coil being adjusted by the impedance adjusting shield so as to match the impedance of the local RF coil and an impedance of the body RF coil, and with a resonance frequency of said local RF coil being adjusted by said frequency modulation element. 
 
     
     
       2. An RF system as claimed in  claim 1  wherein said impedance adjusting shield comprises:
 a hollow casing that fits over said local RF coil, said hollow casing having an open window at one end of said hollow casing, said open window connecting an interior of said hollow casing with an exterior of said hollow casing; and 
 a frequency modulation coil that fits over the end of the hollow casing at which said open window is situated, said open window being inside said frequency modulation coil, and said frequency modulation element being situated on said frequency modulation coil. 
 
     
     
       3. An RF system as claimed in  claim 2  wherein said hollow casing is cylindrical with one open end, with the other end of said hollow casing being said end at which said open window is formed, with said frequency modulation coil coaxially fitting over said other end of said hollow casing. 
     
     
       4. An RF system as claimed in  claim 3  wherein said frequency modulation coil comprises:
 two annular coils coaxially positioned respective at two axial ends of said frequency modulation coil; 
 each annular coil having a circumference at which a plurality of frequency modulation elements are situated; and 
 said frequency modulation coil comprising a plurality of support coils, said support coils each being stripped-shaped and being circumferentially situated between said two annular coils, with two ends of said coils being fixedly connected to said two annular coils, respectively, said support coils each comprising said frequency modulation elements with said frequency modulation elements being situated on said annular coils and positioned between each two adjacent support coils. 
 
     
     
       5. An RF system as claimed in  claim 1  wherein said frequency modulation element is a capacitor. 
     
     
       6. An RF system as claimed in  claim 1  wherein said impedance adjusting shield has a birdcage coil structure, said birdcage coil structure fitting over said local RF coil, and said frequency modulation element being situated in said birdcage coil structure. 
     
     
       7. An RF system as claimed in  claim 6  wherein said birdcage coil construction comprises:
 two annular coils coaxially situated at two axial ends of said birdcage coil structure, each annular coil having a circumference at which a plurality of said frequency modulation elements are situated; and 
 a plurality of support coils, said support coils each being stripped-shaped and being circumferentially situated between said annular coils, said ends of said support coils being fixedly connected to said two annular coils, respectively, and said support coils comprising said frequency modulation elements, with the frequency modulation elements situated on the annular coils between each two adjacent support coils. 
 
     
     
       8. An RF system as claimed in  claim 1  wherein said impedance adjusting shield is comprised of copper. 
     
     
       9. A magnetic resonance (MR) apparatus comprising:
 an MR data acquisition scanner; 
 a radio-frequency (RF) system disposed in said MR data acquisition scanner; and 
 said RF system comprising a local RF coil comprising an inductively coupled coil and a resonator, a body RF coil wirelessly power-coupled with said local RF coil in order for said body RF coil to serve as a transmitting coil for RF signals, and in order for said local coil to serve as a receiving coil for magnetic resonance signals resulting from said RF signals, and an impedance adjusting shield comprising an internal cavity and a frequency modulation element, said local RF coil being disposed in said internal cavity with an impedance of the local coil being adjusted by the impedance adjusting shield so as to match the impedance of the local RF coil and an impedance of the body RF coil, and with a resonance frequency of said local RF coil being adjusted by said frequency modulation element.